Структура текста

Английский текст, как правило, строится по концентрическому принципу, т.е. ключевое предложение каждого абзаца находится в его начале (реже в конце абзаца). Ключевое предложение выражает основную идею данного отрезка текста, а остальные предложения служат для конкретизации, уточнения и иллюстрирования основного высказывания. Поэтому для увеличения скорости чтения и лучшего понимания прочитанного необходимо научиться выделять в тексте смысловые опоры, т.е. ключевые слова и предложения, с помощью которых можно понять основное содержание любого текста.

Упражнение 13. Прочтите следующий текст и составьте план-конспект его содержания. Выпишите ключевые слова, которые понадобятся вам для краткого пересказа содержания текста.

Alkali

The word " alkali" comes from an Ara­bic word meaning " ashes". People used to make alkalis from the ashes of wood and seashore plants, but now they are made in chemical factories. They belong to a class of chemicals called bases.

Bases are the chemical " opposites" of acids. Acids will react with bases to form water and compounds with the general name of salts. This reaction is called neutralization. Most bases are insoluble solids; the few bases that do dissolve in water are called alkalis and are very important chemicals. Alkalis turn litmus paper blue.

Alkalis usually feel slippery to the touch and have a bitter taste. The strongest of them, called caustic alkalis, are dangerously corrosive and destroy human skin and clothing. They must be treated with great care. The commonest are sodium hydroxide (caustic soda), potassium hydroxide (caustic potash), ammonium hydroxide (household ammonia).

Caustic soda is one of the most important alkalis. It is a white compound and is sold commercially as a solid (in flakes and in sticks) or as a solution in water. Large quantities are used in manufacturing soap and in making rayon. It is also used in the cotton industry to give strength and luster to the cotton fibers.

The main industrial use of caustic potash is in the manufacture of soft soaps. Household ammonia helps to remove grease and is used in bath, sink, and window cleaners. Sodium hydrogen carbonate (bicarbonate of soda) is a mild alkali that is used in baking powder, in carbonated drinks, to relieve acidic bee stings, and in medicines designed to neutralize excessive acidity of the stomach.

Most medicines used to relieve " acid stomach", heartburns, and indigestion contain varying amounts of alkalis.